This invention relates to the hydroxylation of olefins. In particular, it relates to a procedure for reacting an olefin, e.g. ethylene or propylene, with an organic hydroperoxide oxidant in the presence of a specific catalyst composition and solvent to produce the corresponding glycol.
It is well known from the technical literature, including patents, that olefins can be effectively oxidized with osmium oxide compounds, particularly osmium tetroxide, to their corresponding diols when the reaction is carried out with organohydroperoxide oxidants and catalytic amounts of osmium tetroxide. However, because of the low activity and/or selectivity of OsO.sub.4 as a catalyst when employed alone, various promoters or co-catalysts have been employed in conjunction with OsO.sub.4 to enhance the rate and/or selectivity of the hydroxylation reaction.
More specifically, Japanese Patent Application No. Sho 54-145604, published Nov. 14, 1979, is directed to a process for hydroxylating olefins in the presence of OsO.sub.4, a quaternary ammonium salt co-catalyst such as tetra ethyl ammonium bromide, and a peroxide including organo peroxides and H.sub.2 O.sub.2 as the oxidant. Selectivities to glycol of from about 4.5 to about 66% are disclosed. It is to be noted, however, that the critical component of the co-catalyst as implied in this patent is the quaternary ammonium cation rather than the particular identity of the anion, since the anion can be any of halogen, hydroxy, nitrate, perchlorate, sulfate, methane sulfonate, trifluoromethane sulfonate, and tetra fluoro borate ions, while the cation must always be quaternary ammonium. Carboxylate anions are not disclosed in this application.
K. B. Sharpless et al, teach in a recent publication J. Org. Chem, Vol. 43 p. 2063 (1978), that tetra alkyl ammonium acetate can be used advantageously as a cocatalyst for the hydroxylation of olefins to corresponding vicinal diols using OsO.sub.4 as a catalyst, and alkyl hydroperoxides as oxidants, provided that the solvent employed is acetone instead of t-butanol, a conventional solvent or co-solvent for such type of reactions. In addition, Sharpless et al disclose the use of excessive amounts of the expensive tetra alkyl ammonium carboxylate salt. The Sharpless et al system from a commercial standpoint is disadvantageous in that the required use of acetone as a solvent complicates the separation of the glycol product, and alcohol by-product derived from the organohydroperoxide oxidant, from the reaction mixture and necessitates the use of additional and expensive distillation equipment required for recycle of the acetone back to the hydroxylation reactor.
The search has therefore continued for co-catalysts which can be employed in conjunction with OsO.sub.4.
Accordingly, it would be of extreme economic significance if co-catalysts could be identified which do not possess the drawbacks of those of the prior art. Commercial olefin hydroxylation systems should be capable of employing as solvents materials which are formed during the hydroxylation reaction and/or materials which are present in commercially available organic hydroperoxides.
For example, during the hydroxylation reaction the organic hydroperoxide, such as t-butyl hydroperoxide (TBHP) will form its corresponding alcohol, such as t-butylalcohol (TBA), as follows, using TBHP as the oxidant, and propylene as the olefin to be hydroxylated: ##STR1## Moreover, commercially available organic hydroperoxides such as TBHP are sold as mixtures of the peroxide and the by-product alcohol TBA. Consequently, a commercial hydroxylation system should not require separation of the by-product alcohol from the reaction mixture before recycle or purification of the commercially available organic hydroperoxide before use.
The search has therefore continued for co-catalysts which can be employed in conjunction with OsO.sub.4 catalyst and organohydroperoxide oxidant to increase the rate and/or selectivity of the hydroxylation reaction in a commercially suitable manner.
The present invention is a result of this search.
Commonly assigned U.S. Pat. No. 4,413,151 by Michaelson, Austin and White, discloses a supported osmium catalyst which can be employed in conjunction with various co-catalysts including carboxylate salts. The description of these salts and their use as co-catalysts in conjunction with OsO.sub.4 is based on the details of the process of the present invention.
While none of the prior art of which applicants are aware disclose the use of carboxylate salts as cocatalysts for use with a H.sub.2 O.sub.2 oxidant in accordance with the present invention, the following patents are discussed to provide a general background of the prior art employing osmium catalysts.
U.S. Pat. No. 2,414,385 discloses the use of hydrogen peroxide and a catalytically active oxide, such as osmium tetroxide, dissolved in an essentially anhydrous non-alkaline, inert, preferably organic, solvent, to convert, by oxidation, unsaturated organic compounds to useful oxygenated products such as glycols, phenols, aldehydes, ketones, quinones and organic acids. The formation of glycols is achieved by conducting the reaction at temperatures of between several degrees below 0.degree. C. and 21.degree. C. Such low reaction temperatures drastically, and disadvantageously, reduce the reaction rate to commercially unacceptable levels. At temperatures greater than 21.degree. C., the formation of aldehydes, ketones and acids is favored.
U.S. Pat. No. 2,773,101 discloses a method for recovering an osmium containing catalyst such as tetroxide, by converting it to the non-volatile osmium dioxide form, distilling the hydroxylation product, reoxidizing the osmium dioxide to the volatile osmium tetroxide, and then recovering the same by distillation. Suitable oxidizing agents used to oxidize olefins, and re-oxidize the osmium dioxide, include inorganic peroxides such as hydrogen peroxide, sodium peroxide, barium peroxide; organic peroxides, such as t-butyl peroxide or hydroperoxide, benzoyl peroxide; as well as other oxidizing agents such as oxygen, perchlorates, nitric acid, chlorine water and the like. As with other methods of the prior art, the above process yields undesirable by-products (see col. 1, line 55) thus reducing the selectivity of the process.
British Patent Specification No. 1,028,940 is directed to a process for regenerating osmium tetroxide from reduced osmium tetroxide by treatment of the latter with molecular oxygen in an aqueous alkaline solution. More specifically, it is disclosed that when osmium tetroxide is used by itself as an oxidizing agent, or as a catalyst in conjunction with other oxidizing agents, to oxidize hydrocarbons, the osmium tetroxide becomes reduced, and in its reduced form is less active than osmium tetroxide itself. Consequently, by conducting the oxidation reaction in the presence of an alkaline medium and supplying oxygen to the medium throughout the process, the osmium tetroxide is maintained in a high state of activity. The oxidation products disclosed include not only ethylene glycol from ethylene but also organic acids from such compounds as vicinal glycols, olefins, ketones and alcohols.
U.S. Pat. No. 4,255,596 is directed to a process for preparing ethylene glycol in a homogeneous single-phase reaction medium using ethylbenzene hydroperoxide as the oxidizing agent dissolved in ethylbenzene and osmium tetroxide as the catalyst. The pH of the reaction medium is maintained at about 14 by the presence of tetraalkyl ammonium hydroxide. A small amount of water can dissolve benefically in the medium to reduce by-product formation and improve selectivity to the glycol.
U.S. Pat. No. 4,049,724 describes the preparation of glycols from alkenes and from unsaturated alcohols in an aqueous system using osmium tetroxide and specifying stable and water-soluble aliphatic hydroperoxides, such as t-butyl hydroperoxide, while a critical pH of 8 to 12 is maintained by a suitable combination of alkali metal buffering compounds. The preparation of propylene glycol utilizing t-butyl hydroperoxide is exemplified in the patent at a selectivity based on the hydroperoxide of 45%.
U.S. Pat. No. 3,335,174 is directed to the use of water hydrolyzable Group Vb, VI-b and VII metal halides and oxyhalides (e.g., OsCl.sub.3) as hydroxylation and esterification catalysts in conjunction with aqueous H.sub.2 O.sub.2 as an oxidant. However, the process for using this catalyst requires the presence of lower aliphatic hydrocarbon acids such as glacial, formic, acetic and propionic acid as solvents. Under these conditions the reaction times vary from 1/2 to 4 hours, but at the shorter reaction times it is disclosed that substantial amounts of epoxide result. The only yield disclosed is obtained in connection with tungsten hexachloride in Example 1. This yield is extremely low, i.e., 22%, and includes both half-acetate and diol. Thus, among the major disadvantages of the process described in this patent are the low selectivities to diol and the corrosiveness of metal halides in the presence of glacial acids such as acetic acid.
See also: U.S. Pat. No. 3,317,592 (discloses production of acids and glycols using oxygen as oxidant, OsO.sub.4 as catalyst at pH 8 to 10); U.S. Pat. No. 3,488,394 (discloses hydroxylation of olefins by reacting olefin and hypochlorite in the presence of OsO.sub.4); U.S. Pat. No. 3,846,478 (discloses reaction of hypochlorite and olefin in an aqueous medium and in the presence of OsO.sub.4 catalyst to hydroxylate the olefin); U.S. Pat. No. 3,928,473 (discloses hydroxylation of olefins to glycols with O.sub.2 oxidant, octavalent osmium catalyst (e.g. OsO.sub.4), and borates as promoter); U.S. Pat. No. 3,391,342 (discloses a process for recovering glycols from an aqueous solution containing alkali metal borate and osmium compounds (e.g. OsO.sub.4); U.S. Pat. No. 3,953,305 (discloses use of OsO.sub.4 catalyst for hydroxylating olefins which is regenerated by oxidizing hexavalent osmium with hexavalent chromium and electro-chemically regenerating hexavalent chromium); U.S. Pat. No. 4,203,926 (discloses ethylbenzene hydroperoxide as oxidant used in two-phase system to hydroxylate olefins in presence of OsO.sub.4 and cesium, rubidium and potassium hydroxides); U.S. Pat. No. 4,217,291 (discloses the oxidation of Osmium (III) or (IV) in an ionic complex with oxygen and an alkali metal, ammonium, or tetra (-lower) alkyl ammonium cation to a valency of greater than +5+organohydroperoxides); U.S. Pat. No. 4,229,601 (discloses the use of cesium, rubidium and potassium hydroxides as promoters for OsO.sub.4 catalyst and t-butyl hydroperoxide oxidant for hydroxylating olefins); and U.S. Pat. No. 4,280,924 (discloses a process for regenerating perosmate catalyst, e.g., cesium, rubidium and potassium perosmate).